A user generally gains possession of an image in two ways; either by downloading this image, or by taking a photograph. The image obtained is ordinarily obtained in a compressed form. The encoding format is imposed, either by the image capture device, or by the provider of the downloaded image, if necessary. However, such a format may not be able to be used by certain software packages or may be in an insufficiently compressed format; having a high compression level is essential when the number of photographs is large, or when the available memory space is small, which is notably the case of portable devices such as digital cameras, cell phones or digital tablets. On the other hand, it may be interesting to keep a photograph in its original format, notably if it is a widespread format such as the JPEG (acronym of Joint Photographic Expert Groups) format, such as it was downloaded or recorded during the image capture; which is contradictory notably with a need for saving space.